Concerns have grown after more than 900 earthquakes have shaken the Tokara islands over almost two weeks, nearly three times the number recorded in similar past events, with the strongest reaching a lower 5 on the Japanese seismic intensity scale.

In total, 911 earthquakes were recorded by the late afternoon on Wednesday, with three registering at shindo lower 5, while 18 reached shindo 4, and the rest were shindo 3, 2 and 1, according to the Japan Meteorological Agency. The strongest quake so far was a magnitude 5.5 recorded at 3:26 p.m. on Wednesday that caused shaking measured at shindo lower 5 in the village of Toshima.

Isamu Sakamoto, head of the local community on Akuseki Island, told The Japan Times via a phone call that he is worried there will be a stronger quake.

¡°I didn¡¯t expect it to be this bad,¡± he said, adding that he does not see an end in sight as he initially thought the quakes would stop after the first shindo lower 5 hit on Monday.

¡°The shaking isn¡¯t horizontal but vertical, and first there¡¯s a loud thud, then it (the ground) starts swaying. It¡¯s very shocking,¡± he said.

Sakamoto, who also runs the local inn, said he has temporarily suspended operations as a safety precaution.

Masashi Kiyomoto, a Meteorological Agency official in charge of earthquakes and tsunamis, said the cause behind the series of earthquakes is still unclear.

¡°Compared to earthquakes two or four years ago, we are experiencing more than twice as many earthquakes that we can feel, but unfortunately, we still don¡¯t know why it is happening or what will happen in the future,¡± he said.

Earlier, a similar shindo lower 5 quake with a magnitude of 5.0 was registered at 4:32 a.m. on Wednesday, among the Tokara islands. No tsunami warning was issued. The quake was at a depth of around 16 kilometers, the agency said.

Kiyomoto said that the risk of tsunami is higher when shallow earthquakes that happen at depths between 10 to 20 km strike at higher magnitudes, and he urges residents to stay alert.

The tremors have been occurring since June 21. They began at around 5 a.m. as weak earthquakes below shindo 1 that were barely felt on the surface. By around 8 a.m., however, quakes strong enough to be felt by residents began increasing in frequency, the agency said.

Similar quakes have struck the islands twice in the past. In 2023, 346 quakes of shindo 1 or greater were recorded in September, and in December 2021, 308 jolts were logged, including a magnitude 6.1 quake that reached shindo upper 5 on Akuseki Island.

As of June 30, the combined population of all seven inhabited Tokara islands was 668 people, according to the Toshima village hall website, including 89 people on Akuseki Island.